Treatment of emulsions

ABSTRACT

A process for separating the components of an emulsion. The process comprises, adjusting the pH of the emulsion to 4 less, adding a coagulant to the emulsion, forming a substantially uniform dispersion of inert particulate carrier in the emulsion adding a polyelectrolyte flocculent either during or after the step of forming the substantially uniform dispersion of inert particulate carrier in the emulsion to form floccs of the inert particulate carrier, the dispersed liquid phase, and the contaminants, allowing the floccs to settle, and separating the relatively clarified continuous liquid phase from the settled floccs.

The present invention relates to the separation of the component of anemulsion.

the term "emulsion" is herein understood to mean a dispersion of aliquid phase in a continuous liquid phase, with either one or both ofthe liquid phases containing contaminants.

One specific example of a relatively complex emulsion is abattoir waste.Abattoir waste comprises a dispersion of a liquid phase of oils, fatsand/or grease (hereinafter referred to as "the oil phase") in an aqueousphase, and further comprises contaminants:

(a) dissolved in the aqueous and/or oil phases;

(b) in particulate form suspended in the aqueous and/or oil phases; or

(c) in colloidal form in the aqueous and/or oil phases.

The contaminants include bacteria count, nutrients, BOD, sand, grit andfaeces.

Abattoir waste does not satisfy the environmental requirements fordisposal into river and stream systems and thus has to be treated toseparate the oil phase from the aqueous phase and to remove thecontaminants from the aqueous phase before disposal of the aqueous phaseis possible. Generally, such treatment includes transferring theabattoir waste through a series of aerobic and anaerobic dams. This isnot an altogether satisfactory treatment regime in view of the set-upand on-going costs involved. A further disadvantage is that thetreatment is not adapted to recover economically valuable contaminants,such as dissolved protein, in the abattoir waste.

Another specific example of a relatively complex emulsion is mineral oilwaste from de-greasing units widely used in industry. Typically, in suchunits suitable solvents are sprayed onto equipment to dissolve theoil/grease on the equipment, water is then sprayed onto the equipment toremove the dissolved oil/grease and remaining solvent, and the resultantemulsion, which by this stage includes grit and other contaminants, iscollected in a sump and pumped to a settling pond.

Mineral oil waste does not satisfy the environmental requirements fordisposal into river and stream systems and thus has to be treated toseparate the oil/grease phase from the aqueous phase and to remove thesolid and liquid contaminants from the aqueous phase before disposal ofthe aqueous phase is possible. At present there is no altogethersatisfactory cost-effective treatment regime for this purpose.

An object of the present invention is to provide a process forseparating the components of an emulsion.

A more particular object of the present invention is to provide aprocess for separating the components of complex emulsions comprising anoil-based liquid phase dispersed in a continuous aqueous phase, such asabattoir waste, mineral oil waste, dairy waste and food waste, to allowthe aqueous phase to be released into river and stream systems.

According to the present invention there is provided a process forseparating the components of an emulsion, as described herein,comprising the following steps in sequence:

(a) adjusting the pH of the emulsion to be 4 or less;

(b) adding a coagulant to the emulsion;

(c) forming a substantially uniform dispersion of inert particulatecarrier in the emulsion;

(d) adding a polyelectrolyte flocculent either during or after the stepof forming the substantially uniform dispersion of inert particulatecarrier in the emulsion to form floccs of the inert particulate carrier,the dispersed liquid phase, and the contaminants;

(e) allowing the floccs to settle; and

(f) separating the relatively clarified continuous liquid phase from thesettled floccs.

The basis of the present invention is that it has been foundunexpectedly that adjustment of the pH of an emulsion, such as abattoirwaste, to 4 or less and the addition of a coagulant has the effect ofconditioning the emulsion so that inert particulate carrier andflocculent can separate the dispersed liquid phase and the contaminants,including dissolved contaminants, from the continuous liquid phase ofthe emulsion. The unexpected finding is derived from the combined effectof acid and coagulant being greater than the separate effect of acid andcoagulant.

The term "inert" as used herein in relation to "particulate carrier" isunderstood to mean that the particulate carrier is not substantiallyattacked by the emulsion. In other words, the term "inert" means thatthe particulate carrier exhibits both suitable chemical and physicalstability in the emulsion.

It is preferred that the flocculent is a polyelectrolyte flocculent. Theterm "polyelectrolyte flocculent" as used herein is understood to meanany suitable cationic, non-ionic and anionic flocculent.

It is preferred that the pH is adjusted to be 3.5 or less.

It is preferred that the pH is adjusted to 3 or less.

It is preferred that the process further comprises adjusting the pH ofthe emulsion to be 5 or more after the addition of the coagulant in step(b) above.

It is particularly preferred that the pH is adjusted to be 5.5 or moreafter the addition of the coagulent in step (b) above.

It is preferred that the process further comprises processing the floccsto separate the inert particulate carrier from the dispersed liquidphase and the contaminants. It is particularly preferred that theprocess further comprises classifying the contaminants into valuablecomponents.

It is preferred that the emulsion comprises a dispersion of an oil-basedliquid phase in a continuous aqueous phase.

It is particularly preferred that the emulsion comprises abattoir waste,mineral oil waste, dairy waste, or food waste.

It is preferred that the coagulant comprises aluminium salts, ferroussalts or ferric salts.

It is preferred that the inert particulate carrier is selected from thegroup comprising sand, alumina, garnet, magnetite, hematite, ilmeniteand calcite.

The process of the present invention is described further with referenceto the following examples.

EXAMPLE 1

A series of samples of emulsified mineral oil waste from a de-greaserunit were treated in accordance with a preferred embodiment of theprocess of the present invention. The principal objective of theexperimental work was to assess the extent to which the process of thepresent invention could separate the aqueous component from the mineraloil waste.

The mineral oil waste samples contained a dispersion of oil and greasein a continuous aqueous phase and the contaminants at the levels set outin Table 1 below.

                  TABLE 1                                                         ______________________________________                                                          mg/l                                                        ______________________________________                                        Total Suspended Solids                                                                            350                                                       Benzene             <1                                                        Toluene             <1                                                        Xylene              <1                                                        Polynuclear Aromatic                                                                              230                                                       Hydrocarbons                                                                  Chemical Oxygen Demand                                                                            2570                                                      Biological Oxygen Demand                                                                          110                                                       ______________________________________                                    

The samples of the mineral oil waste were treated as follows.

1. Adjustment of the pH to between 2.5 and 3.5.

2. Addition of a coagulant-sodium aluminate.

3. Adjustment of pH to between 5.5 and 7.5.

4. Agitating the mineral oil waste and inert particulate carrier to forma uniform dispersion of inert particulate carrier in the mineral oilwaste.

5. Addition of a polyelectrolyte flocculent (Zetag 92--produced byAllied Colloids) to form floccs of oil/grease, contaminants listed inTable 1, inert particulate carrier, and polyelectrolyte flocculent.

6. Separation of the floccs and the liquor.

The samples of the liquor recovered from step 6 above were tested andfound to be water with no visible oil/grease and with contaminants atthe levels set out in Table 2 below.

                  TABLE 2                                                         ______________________________________                                                          mg/l                                                        ______________________________________                                        Total Suspended Solids                                                                            7                                                         Benzene             <1                                                        Toluene             <1                                                        Xylene              <1                                                        Polynuclear Aromatic                                                                              <0.1                                                      Hydrocarbons                                                                  Chemical Oxygen Demand                                                                            550                                                       Biological Oxygen Demand                                                                          90                                                        ______________________________________                                    

The results of the experimental work indicate clearly that the preferredembodiment of the process of the present invention is capable ofseparating the aqueous phase of the mineral oil waste from theoil/grease phase and substantially removing the contaminants from theaqueous phase.

EXAMPLE 2

A series of samples of abattoir waste were treated in accordance with apreferred embodiment of the process of the present invention. Theprincipal purpose of the experimental work was to assess the extent towhich the process of the present invention could separate the aqueouscomponent from the abattoir waste.

The abattoir waste samples contained a dispersion of 85 mg/l of oil andgrease in a continuous aqueous phase and the contaminants at the levelsset out in Table 3 below.

                  TABLE 3                                                         ______________________________________                                                          mg/l                                                        ______________________________________                                        Total Suspended Solids                                                                            2,700                                                     Total Phosphorus    30.5                                                      Chemical Oxygen Demand                                                                            29.9                                                      Biological Oxygen Demand                                                                          1850                                                      Total Kjeldahl Nitrogen                                                                           175                                                       ______________________________________                                    

The samples of abattoir waste were treated as follows:

1. Adjustment of pH to between 2.5 and 3.5.

2. Addition of a coagulant--sodium aluminate.

3. Adjustment of pH to between 5.5 and 7.5.

4. Agitating the abattoir waste and inert particulate carrier to form auniform dispersion of inert particulate carrier.

5. Addition of polyelectrolyte flocculent (Zetag 92--produced by AlliedColloids) to form floccs of oil and grease, contaminants listed in Table3, inert particulate carrier, and polyelectrolyte flocculent.

6. Separation of the floccs and the liquor.

The samples of the liquor recovered from step 6 above were tested andfound to have only 5 mg/l oil and grease and the contaminants at levelsset out in Table 4 below.

                  TABLE 4                                                         ______________________________________                                                          mg/l                                                        ______________________________________                                        Total Suspended Solids                                                                            45                                                        Total Phosphorus    0.85                                                      Chemical Oxygen Demand                                                                            *ND                                                       Biological Oxygen Demand                                                                          220                                                       Total Kjeldahl Nitrogen                                                                           30                                                        ______________________________________                                         *ND -- not determined                                                    

The results of the experimental work indicate clearly that the preferredembodiment of the process of the present invention is capable ofsubstantially separating the aqueous phase of the abattoir waste fromthe oil/grease phase and substantially removing the contaminants fromthe aqueous phase to a level at which the aqueous phase is safe fordisposal in river and stream systems.

Many modifications may be made to the process of the present inventionas described above without departing from the spirit and scope of thepresent invention.

In this regard, it is noted that the step of adjusting the pH to between5.5 and 7.5 after the initial acidification and coagulant addition stepsis not an essential step of the process of the invention and wasnecessary as part of the procedure in the examples in order to ensuretotal removal of the aluminium based coagulant and optimum performanceof the particular polyelectrolyte used in the examples.

I claim:
 1. A process for treating an emulsion comprising a dispersedoil-based liquid phase in a continuous aqueous liquid phase, either ofthe dispersed liquid phase and the continuous liquid phase containingcontaminants, the process comprising the steps of:(a) adjusting the pHof the emulsion to be 3.5 or less; (b) adding a coagulant selected formthe group consisting of aluminum salts, ferrous salts and ferric saltsto the emulsion; (c) adjusting the pH of the emulsion to be 5 or moreafter the addition of the coagulant in step (b) and forming asubstantially uniform dispersion of inert particulate carrier selectedfrom the group consisting of sand, alumina, garnet, magnetite, hematite,ilmenite and calcite in the emulsion; (d) adding a polyelectrolyteflocculent either during or before the step of forming the substantiallyuniform dispersion of inert particulate carrier in the emulsion to formfloccs of the inert particulate carrier, the dispersed liquid phase, andthe contaminants; (e) allowing the floccs to settle; and (f) separatingthe relatively clarified continuous liquid phase from the settledfloccs.
 2. The process defined in claim 1, comprising adjusting the pHto be 3 or less.
 3. The process defined in claim 1, comprising adjustingthe pH of the emulsion to be 5.5 or more after the addition of thecoagulant in step (b) above.
 4. The process defined in claim 1, furthercomprising processing the floccs to separate the inert particulatecarrier from the dispersed liquid phase and the contaminants.
 5. Theprocess defined in claim 1, further comprising classifying thecontaminants in the settled floccs.
 6. The process defined in claim 1,wherein the emulsion comprises abattoir waste, mineral oil waste, dairywaste, or food waste.